The present invention is exemplified by a high voltage coil for projection television systems, but it should be understood that the present coil may find utility in a variety of high voltage coil applications where a plurality of electrically isolated coils are formed on the same coil form.
In the past two methods have been employed in the manufacture of high voltage coils. The first utilizes an automatic coil winding machine that wraps layers of coil wire, terminating each coil on pins on coil form end plates. After each coil is wound, and at the same station, a plurality of layers of Mylar insulator are wrapped on each coil by an automated winding device.
While this process has acheived a significant degree of commercial success, it has several disadvantages. One is that the Mylar insulators, because they are wrapped by automatic winding machinery, are wound so tightly against its own layers, against the underlying coil and also against the coil formed end plates, that complete impregnation by fluid epoxy, even by advanced vacuum impregnation techniques is not possible on a consistent basis.
The second method of making these high voltage coils is to wind the coils, not on the final coil form with end plates, but instead on separate insulator tubes having increasing diameters so that they may be subsequently concentrically mounted. Then, beginning with the smallest tube and coil assembly, they ate inserted over a coil form with one of the end plates removed. Then, the additional incrementally larger coil and tube assemblies are slid serially over one another until the desired number of coils and tubes are mounted. The previously removed end plate is then reattached to the coil form and the respective coils are terminated at the opposite end plate terminals.
This method, to some extent, ameliorates the problems noted above in the wrapping method because the diameter of the tubes with respect to the outer diameter of the underlying coil can be varied as desired to achieve potting material flow. However, it is diffucult to control the axial gap between the tubes and the end plates and between the coils and the end plates because the tube and coils are formed without the end plates in situ, so that while the inner diameter of the various insulating tubes can be controlled, complete impregnation is not consistently possible because there is no effective way for the epoxy to get down into the coils at the various radial levels of these concentric tubes.
The second method also requires a significant amount of assembly time because the coil is effectively formed in two stages.
It is a primary object of the present invention to ameliorate the problems described above in high voltage coils and their method of manufacture.